public void handleStep(StepInterpolator interpolator, boolean isLast)
        throws DerivativeException {

      ++nbSteps;
      for (int a = 1; a < 100; ++a) {

        double prev = interpolator.getPreviousTime();
        double curr = interpolator.getCurrentTime();
        double interp = ((100 - a) * prev + a * curr) / 100;
        interpolator.setInterpolatedTime(interp);

        double[] interpolatedY = interpolator.getInterpolatedState();
        double[] theoreticalY = pb.computeTheoreticalState(interpolator.getInterpolatedTime());
        double dx = interpolatedY[0] - theoreticalY[0];
        double dy = interpolatedY[1] - theoreticalY[1];
        double error = dx * dx + dy * dy;
        if (error > maxError) {
          maxError = error;
        }
      }
      if (isLast) {
        assertTrue(maxError < 2.7e-6);
        assertTrue(nbSteps < 80);
      }
    }
    public void handleStep(StepInterpolator interpolator, boolean isLast) {

      double step = Math.abs(interpolator.getCurrentTime() - interpolator.getPreviousTime());
      if (firstTime) {
        minStep = Math.abs(step);
        maxStep = minStep;
        firstTime = false;
      } else {
        if (step < minStep) {
          minStep = step;
        }
        if (step > maxStep) {
          maxStep = step;
        }
      }

      if (isLast) {
        assertTrue(minStep < 8.2e-3);
        assertTrue(maxStep > 1.7);
      }
    }